42 NON-MARINE FOSSIL MOLLUSCA. 



This species is similar in outward form to those which have been 

 grouped under the subgeneric name of Gyraulus; but in size it is very 

 much greater than any of the species which have been referred to that 

 subgenus. 



A species somewhat similar to the last, but smaller, more nearly discoid 

 in form, and having much more slender volutions, was obtained by my- 

 self from the Green Eiver Group of Southern Wyoming, and described 

 under the name of Planorhis cirratus.* It is illustrated on Plate 29. 

 From the same region and from the same formation I also obtained Plan- 

 orhis cequalis White, t which is illustrated on Plate 29. It seems to 

 possess all the characteristics of the typical section of the genus. 



Prom the fresh- water strata that are referred to the Miocene epoch, 

 ouly four species of Planorhis have yet been published, which, being the 

 only known fossil species of that genus of later date than the Eocene, 

 are the remaining species to be noticed in this article. Three of these 

 are described by Meek & Hayden from the White Eiver Group in 

 Dakota, under the names respectively of Planorhis vetustus, P. leidyi, and 

 P. nebrascensis.% They are illustrated on Plate 32. The remaining 

 species§ was described by T. A. Conrad, under the name of P. lunatus, 

 from "Bridge Creek, Oregon," where it was found- associated with 

 Zonites marginicola, mentioned on a following page. Copies of Conrad's 

 figure are given on Plate 32. 



Eeference has already been made, in connection with a notice of Sphw- 

 riuin rugosum and S.f idahoense, to two deposits similar to each other 

 in their faunal contents, the one being found in the neighborhood of the 

 Kawsoh Mountains, in Northern Nevada, and the other in Southern 

 Idaho, which are regarded as of Miocene age. These strata have fur- 

 nished a limited but interesting molluscau fauna, among the species of 

 which are two that wer^ described by Meek under the names respect- 

 ively of Carinifex (Vorticifex) tryoni and C. (V.) binneyi.\\ . Both these 

 forms are illustrated on Plate 32. 



Although, as has already been shown, the family Linmseidai (to which 

 Carinifex is here referred) flourished ever since Mesozoic time, no other 

 fossil species of Carinifex have yet been found in strata of any age, and 

 no representatives of that genus are now known to be living in North 

 America except a few upon the Pacific slope. If the Miocene lake, the 

 deposits of which contain the two species of Carinifex which have just 

 been noticed, had drained into what is now the hydrographic basin of 

 the Mississippi, representatives of that type as well as those of its asso- 

 ciate mollusca would no doubt now be found living there. But as the 



* Au. Kep. U. S. Geol. Sur. Terr, for 1878, Part I, p. 44, pi. 19, tig. 5. 

 t Proceedings U. S. Nat. Museum, vol. iii, p. 159. 



t For descriptions and figures of these three species by their authors, see U. S. Geol. 

 Sur. Terr., vol. ix, pp. 600, 001, pi. 45, figs. 1, 2, and 3. 

 $ Am. Jour. Couch, vol. vi, p. 315, pi. 13, fig. 8. 

 || U. S. Geol. Sur. 40th Parallel, vol. iv, pp. 187, 188, pi. xvii, figs. 11 and 12. 



